The present invention relates to an improved method of disinfecting a soft lens with a stabilized aqueous hydrogen peroxide solution having a hydrogen peroxide content from about 0.5 to about 6% by weight hydrogen peroxide wherein the stabilized solution contains from about 0.003 and about 0.03% by weight of diethylene triamine penta (methylenephosphonic acid) or a physiologically compatable salt thereof.
Soft contact lenses are characteristically prepared from hydrophilic polymers, such as polymers of hydroxyethyl methacrylate (HEMA), crosslinked with a conventional crosslinking agent, such as ethylene glycol dimethacrylate (EGDMA), or more complex copolymer systems including copolymers of HEMA, EGDMA, methacrylic acid and/or poly-N-vinylpyrrolidone, and the like. Other hydrophilic monomers conventionally employed in varying amounts in the manufacture of soft contact lenses include, for example, N-vinylpyrrolidone, glyceryl methacrylate, diethylene glycol monomethacrylate, triethylene glycol monomethacrylate, allyl 2-hydroxyethyl ether, acrylic acid, acrylamide, N,N-dimethylacrylamide, and the like. Other conventional crosslinking agents commonly employed include, inter alia, diallyl ether, divinyl benzene, diethylene glycol dimethacrylate, triethylene glycol dimethacrylate, diallyl succinate, allyl methacrylate, glycerin tri-methacrylate, and the like. Moreover, various amounts of relatively hydrophobic monomer units can be employed in the manufacture of soft contact lens materials, as long as the final copolymer network exhibits the desired hydrophilic characteristics. Typical hydrophobic monomers include methyl methacrylate, glycidyl methacrylate, N-(1,1-dimethyl-3-oxobutyl)acrylamide, siloxane methacrylates, perfluoroalkyl methacrylates, perfluoroalkoxyperfluoroalkyl methacrylates, and the like. In general, such lenses exhibit marked hydrophilic properties and, when wet, absorb water and are soft and flexible.
While these lenses are not actually perforate, they do have a sufficient degree of molecular porosity to permit water, oxygen and tear fluids to permeate the lens structure. In order for the disinfection of such lenses to be effective after they have been worn, it is important that contaminants be removed from both surfaces, and the interior of the lens, to the extent contaminants are present therein. Hydrogen peroxide in the form of a dilute solution, e.g. about 0.5 to 6% by weight in water, is known to be effective for use with contact lenses in order to kill any contaminating microorganisms.
One drawback with unstabilized dilute hydrogen peroxide solutions, however, is that without the use of a stabilizer or a combination of stabilizers, the aqueous peroxide solutions characteristically decompose over a period of time. The rate at which such dilute hydrogen peroxide solutions decompose will, of course, be dependent upon such factors as pH and the presence of trace amounts of various metal impurities, such as copper or chromium, which may act to catalytically decompose the same. Moreover, at moderately elevated temperatures the rate of decomposition of such dilute aqueous hydrogen peroxide solutions is greatly accelerated.
A large variety of stabilizers have been proposed for use with hydrogen peroxide to deactivate trace catalytic impurities, including stannous salts, ethylene diamine tetracetic acid, and the like.
For example, U.S. Pat. No. 3,860,391 discloses bleaching both compositions containing hydrogen peroxide and, as a stabilizer, amino lower alkylene polyphosphates, including diethylene triamine penta (methylenephosphinic acid) or salts thereof, and/or hydroxy alkane phosphates, with or without additional stabilizer constituents, and adjusted to a pH of between about 9.0 and 12.0 with, e.g. sodium hydroxide, for the bleaching of cellulose materials. Exemplified are compositions having a pH of 12.0.
Unfortunately, such highly basic compositions are undesirable in a contact lens environment and especially in th disinfection of contact lenses.
Thus, it is essential that the hydrogen peroxide containing solutions employed be, upon disinfection of the contact lenses and decompositon of the hydrogen peroxide, sufficiently compatable with the ocular environment so as not to occasion ocular irritation or damage if the disinfected contact lens containing the residual solution absorbed by the lens, is placed into the eye.
Caustic compositions, for example, can occasion severe ocular irritation and damage to the ocular tissue.
It is thus an object of the present invention to provide a method of disinfecting a soft contact lens with a stabilized aqueous hydrogen peroxide solution having a pH of about 5 to about 7, employing diethylene triamine penta (methylenephosphinic acid) or a physiologically compatable salt thereof, as a stabilizer, such that upon disinfection of such contact lens and decomposition of residual hydrogen peroxide, the resulting solution, absorbed by and adhering to said lens, is physiologically tolerable to the ocular environment.
It is a further object of the present invention to provide stabilized aqueous hydrogen peroxide solutions for use in such method.
These and other objects of the present invention are apparent from the following more specific disclosures.